Devices for holding an amount of magnetic fluid by means of a magnetic field inside a gap-shaped space located around a rotatable shaft have been proposed. They include a unit consisting of an annular pole piece whose inner circumferential plane is located a relatively short distance from the shaft. These devices include at least one annular permanent magnet for generating the magnetic field, whereby the magnetic fluid is kept inside the gap-shaped space formed between this unit and the shaft. A similar device in the shape of a sealing unit is disclosed in European Patent Application 0182656.
This prior art unit includes one annular permanent magnet located around the shaft and, located on either side of this magnet, two pole pieces each of which, together with the shaft, form an annular sealing gap in which an amount of magnetic fluid is held by the magnetic field of the magnet. This means that the known unit is relatively complicated because of the presence of two sealing gaps.
Although the publication mentioned states that at least one pole piece is required, a similar unit with only one pole piece has not been at all adequate in practice because the asymmetrical design of the unit the magnetic field inside the sealing gap is not capable of keeping the magnetic fluid inside the gap under all circumstances. These prior art units are inoperative in some circumstances.
Accordingly, an object of the present invention is to create an improved bearing unit of the type mentioned with a considerably simpler design. Other objects will appear hereinafter.